Functionalized polymer, rubber composition and pneumatic tire

ABSTRACT

The present invention is directed to a functionalized elastomer comprising the reaction product of a living anionic elastomeric polymer and a polymerization terminator of formula I 
                         
wherein R 1  is C1 to C4 linear alkyl, or C1 to C4 branched alkanediyl; X 1 , X 2 , X 3  are independently O, S, or a group of formula (II) or (III)
 
                         
where R 2  is C1 to C18 linear or branched alkyl; and Z is —R 3 —CH═CH—R 4 , where R 3  is a covalent bond or C1 to C18 linear or branched alkanediyl, and R 4  is a hydrogen or C1 to C18 linear or branched alkyl.

BACKGROUND OF THE INVENTION

In recent years, there is a growing demand for functionalized polymers.Functionalized polymers can be synthesized through variousliving/controlled polymerization techniques. In the livingpolymerization process, based on an active carbanionic center, metalsfrom Groups I and II of the periodic table are commonly used to initiatethe polymerization of monomers into polymers. For example, lithium,barium, magnesium, sodium, and potassium are metals that are frequentlyutilized in such polymerizations. Initiator systems of this type are ofcommercial importance because they can be used to producestereoregulated polymers. For instance, lithium initiators can beutilized to initiate the anionic polymerization of isoprene intosynthetic polyisoprene rubber or to initiate the polymerization of1,3-butadiene into polybutadiene rubber having the desiredmicrostructure.

The polymers formed in such polymerizations have the metal used toinitiate the polymerization at the growing end of their polymer chainsand are sometimes referred to as living polymers. They are referred toas living polymers because their polymer chains, which contain theterminal metal initiator, continue to grow or live until all of theavailable monomer is exhausted. Polymers that are prepared by utilizingsuch metal initiators normally have structures which are essentiallylinear and normally do not contain appreciable amounts of branching.

This invention details the synthesis of functionalized polymers andtheir use in rubber formulation and tire materials. Often, to achievethe best tire performance properties, functionalized polymers are highlydesirable. In order to reduce the rolling resistance and to improve thetread wear characteristics of tires, functionalized elastomers having ahigh rebound physical property (low hysteresis) have been used for thetire tread rubber compositions. However, in order to increase the wetskid resistance of a tire tread, rubbery polymers that have a relativelylower rebound physical property (higher hysteresis) which therebyundergo a greater energy loss, have sometimes been used for such treadrubber compositions. To achieve these desired viscoelastic propertiesfor the tire tread rubber compositions, blends (mixtures) of varioustypes of synthetic and natural rubber can be utilized in tire treads.

Functionalized rubbery polymers made by living polymerization techniquesare typically compounded with sulfur, accelerators, antidegradants, afiller (such as carbon black, silica or starch) and other desired rubberchemicals. These are then subsequently vulcanized or cured into the formof a useful article, such as a tire or a power transmission belt. It hasbeen established that many physical properties of such cured rubbersdepend upon the degree to which the filler is homogeneously dispersedthroughout the rubber. This is, in turn, related to the level ofaffinity that filler has for the particular rubbery polymer. This can beof practical importance in improving the physical characteristics ofrubber articles which are made utilizing such rubber compositions. Forexample, the rolling resistance and traction characteristics of tirescan be improved by improving the affinity of carbon black and/or silicato the rubbery polymer utilized therein. Therefore, it would be highlydesirable to improve the affinity of a given rubbery polymer forfillers, such as carbon black and silica.

In tire tread formulations, better interaction between the filler andthe rubbery polymer results in lower hysteresis and consequently tiresmade with such rubber formulations have lower rolling resistance. Lowtan delta values at 60° C. are indicative of low hysteresis andconsequently tires made utilizing such rubber formulations with low tandelta values at 60° C. normally exhibit lower rolling resistance. Betterinteraction between the filler and the rubbery polymer in tire treadformulations also typically results in higher tan delta values at 0° C.which is indicative of better traction characteristics.

The interaction between rubber and carbon black has been attributed to acombination of physical absorption (van der Waals force) andchemisorption between the oxygen containing functional groups on thecarbon black surface and the rubber (see D. Rivin, J. Aron, and A.Medalia, Rubber Chemical & Technology 41, 330 (1968) and A. Gessler, W.Hess, and A Medalia, Plastic Rubber Process, 3, 141 (1968)). Variousother chemical modification techniques, especially for styrene-butadienerubber made by solution polymerization (S-SBR), have also been describedfor reducing hysteresis loss by improving polymer-filler interactions.In one of these techniques, the solution rubber chain end is modifiedwith aminobenzophenone. This greatly improves the interaction betweenthe polymer and the oxygen-containing groups on the carbon black surface(see N. Nagata, Nippon Gomu Kvokaishi, 62, 630 (1989)). Tin coupling ofanionic solution polymers is another commonly used chain endmodification method that aids polymer-filler interaction supposedlythrough increased reaction with the quinone groups on the carbon blacksurface. The effect of this interaction is to reduce the aggregationbetween carbon black particles which in turn, improves dispersion andultimately reduces hysteresis.

SUMMARY OF THE INVENTION

The subject invention provides a low cost means for the end-groupfunctionalization of rubbery living polymers to improve their affinityfor fillers, such as carbon black and/or silica. Such functionalizedpolymers can be beneficially used in manufacturing tires and otherrubber products where improved polymer/filler interaction is desirable.In tire tread compounds this can result in lower polymer hysteresiswhich in turn can provide a lower level of tire rolling resistance.

The present invention is directed to a functionalized elastomercomprising the reaction product of a living anionic elastomeric polymerand a polymerization terminator of formula I

wherein R¹ is C1 to C4 linear alkanediyl, or C1 to C4 branchedalkanediyl; X¹, X², X³ are independently O, S, or a group of formula(II) or (III)

where R² is C1 to C18 linear or branched alkyl; and Z is —R³—CH═CH—R⁴,where R³ is a covalent bond or C1 to C18 linear or branched alkane diyl,and R⁴ is a hydrogen or C1 to C18 linear or branched alkyl; wherein Q isnitrogen.

The invention is further directed to a rubber composition comprising thefunctionalized elastomer, and a pneumatic tire comprising the rubbercomposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a graph of torque versus cure time for several rubbersamples.

FIG. 2 shows a graph of G′ versus percent strain for several rubbersamples.

FIG. 3 shows a graph of tan delta versus percent strain for severalrubber samples.

DETAILED DESCRIPTION OF THE INVENTION

There is disclosed a functionalized elastomer comprising the reactionproduct of a living anionic elastomeric polymer and a polymerizationterminator of formula I

wherein R¹ is C1 to C4 linear alkyl, or C1 to C4 branched alkanediyl;X¹, X², X³ are independently O, S, or a group of formula (II) or (III)

where R² is C1 to C18 linear or branched alkyl; and Z is —R³—CH═CH—R₄,where R³ is a covalent bond or C1 to C18 linear or branched alkane diyl,and R⁴ is a hydrogen or C1 to C18 linear or branched alkyl.

There is further disclosed a rubber composition comprising thefunctionalized elastomer, and a pneumatic tire comprising the rubbercomposition.

The subject invention provides a means for the end-groupfunctionalization of rubbery living polymers to improve their affinityfor fillers, such as carbon black and/or silica. The process of thepresent invention can be used to functionalize any living polymer whichis terminated with a metal of group I or II of the periodic table. Thesepolymers can be produced utilizing techniques that are well known topersons skilled in the art. The metal terminated rubbery polymers thatcan be functionalized with a terminator of formula I in accordance withthis invention can be made utilizing monofunctional initiators resultingin polymers having the general structural formula P-M, wherein Prepresents a polymer chain and wherein M represents a metal of group Ior II. The metal initiators utilized in the synthesis of such metalterminated polymers can also be multifunctional organometalliccompounds. For instance, difunctional organometallic compounds can beutilized to initiate such polymerizations. The utilization of suchdifunctional organometallic compounds as initiators generally results inthe formation of polymers having the general structural formula M-P-M,wherein P represents a polymer chain and wherein M represents a metal ofgroup I or II. Such polymers, which are terminated at both of theirchain ends with a metal from group I or II, also can be reacted withterminator of formula I to functionalize both of their chain ends. It isbelieved that utilizing difunctional initiators so that both ends of thepolymers chain can be functionalized with the terminator of formula Ican further improve interaction with fillers, such as carbon black andsilica.

The initiator used to initiate the polymerization employed insynthesizing the living rubbery polymer that is functionalized inaccordance with this invention is typically selected from the groupconsisting of barium, lithium, magnesium, sodium, and potassium.Reagents consisting of barium, lithium, magnesium, sodium, and potassiumalkyls may also be used. Lithium and magnesium are the metals that aremost commonly utilized in the synthesis of such metal terminatedpolymers (living polymers). Normally, alkyllithium initiators are morepreferred.

Organolithium compounds are the preferred initiators for utilization insuch polymerizations. The organolithium compounds which are utilized asinitiators are normally organo monolithium compounds. The organolithiumcompounds which are preferred as initiators are monofunctional compoundswhich can be represented by the formula: R—Li, wherein R represents ahydrocarbyl radical containing from 1 to about 20 carbon atoms.Generally, such monofunctional organolithium compounds will contain from1 to about 10 carbon atoms. Some representative examples of preferredreagents are butyllithium, secbutyllithium, n-hexyllithium,n-octyllithium, tertoctyllithium, n-decyllithium, phenyllithium,1-naphthyllithium, 4-butylphenyllithium, p-tolyllithium,4-phenylbutyllithium, cyclohexyllithium, 4-butylcyclohexyllithium, and4-cyclohexylbutyllithium. Secondary butyllithium is a highly preferredorganolithium initiator. Very finely divided lithium having an averageparticle diameter of less than 2 microns can also be employed as theinitiator for the synthesis of living rubbery polymers that can befunctionalized with a terminator of formula I in accordance with thisinvention. U.S. Pat. No. 4,048,420, which is incorporated herein byreference in its entirety, describes the synthesis of lithium terminatedliving polymers utilizing finely divided lithium as the initiator.Lithium amides can also be used as the initiator in the synthesis ofliving polydiene rubbers (see U.S. Pat. No. 4,935,471, the teaching ofwhich are incorporated herein by reference with respect to lithiumamides that can be used as initiators in the synthesis of living rubberypolymer).

The amount of organolithium initiator utilized will vary depending uponthe molecular weight which is desired for the rubbery polymer beingsynthesized as well as the precise polymerization temperature which willbe employed. The precise amount of organolithium compound required toproduce a polymer of a desired molecular weight can be easilyascertained by persons skilled in the art. However, as a general rulefrom 0.01 to 1 phm (parts per 100 parts by weight of monomer) of anorganolithium initiator will be utilized. In most cases, from 0.01 to0.1 phm of an organolithium initiator will be utilized with it beingpreferred to utilize 0.025 to 0.07 phm of the organolithium initiator.

Many types of unsaturated monomers which contain carbon-carbon doublebonds can be polymerized into polymers using such metal catalysts.Elastomeric or rubbery polymers can be synthesized by polymerizing dienemonomers utilizing this type of metal initiator system. The dienemonomers that can be polymerized into synthetic rubbery polymers can beeither conjugated or non-conjugated diolefins. Conjugated diolefinmonomers containing from 4 to 8 carbon atoms are generally preferred.Vinyl-substituted aromatic monomers can also be copolymerized with oneor more diene monomers into rubbery polymers, for examplestyrene-butadiene rubber (SBR). Some representative examples ofconjugated diene monomers that can be polymerized into rubbery polymersinclude 1,3-butadiene, isoprene, 1,3-pentadiene,2,3-dimethyl-1,3-butadiene, 2-methyl 1,3-pentadiene,2,3-dimethyl-1,3-pentadiene, 2-phenyl-1,3-butadiene, and4,5-diethyl-1,3-octadiene. Some representative examples ofvinyl-substituted aromatic monomers that can be utilized in thesynthesis of rubbery polymers include styrene, 1-vinylnapthalene,3-methylstyrene, 3,5-diethylstyrene, 4-propylstyrene,2,4,6-trimethylstyrene, 4-dodecylstyrene,3-methyl-5-normal-hexylstyrene, 4-phenylstyrene,2-ethyl-4-benzylstyrene, 3,5-diphenylstyrene, 2,3,4,5-tetraethylstyrene,3-ethyl-1-vinylnapthalene, 6-isopropyl-1-vinylnapthalene,6-cyclohexyl-1-vinylnapthalene, 7-dodecyl-2-vinylnapthalene,o-methylstyrene, and the like.

The metal terminated rubbery polymers that are functionalized with aterminator of formula I in accordance with this invention are generallyprepared by solution polymerizations that utilize inert organicsolvents, such as saturated aliphatic hydrocarbons, aromatichydrocarbons, or ethers. The solvents used in such solutionpolymerizations will normally contain from about 4 to about 10 carbonatoms per molecule and will be liquids under the conditions of thepolymerization. Some representative examples of suitable organicsolvents include pentane, isooctane, cyclohexane, normal-hexane,benzene, toluene, xylene, ethylbenzene, tetrahydrofuran, and the like,alone or in a mixture. For instance, the solvent can be a mixture ofdifferent hexane isomers. Such solution polymerizations result in theformation of a polymer cement (a highly viscous solution of thepolymer).

The metal terminated living rubbery polymers utilized in the practice ofthis invention can be of virtually any molecular weight. However, thenumber average molecular weight of the living rubbery polymer willtypically be within the range of about 50,000 to about 500,000. It ismore typical for such living rubbery polymers to have number averagemolecular weights within the range of 100,000 to 250,000.

The metal terminated living rubbery polymer can be functionalized bysimply adding a stoichiometric amount of a terminator of formula I to asolution of the rubbery polymer (a rubber cement of the living polymer).In other words, approximately one mole of the terminator of formula I isadded per mole of terminal metal groups in the living rubbery polymer.The number of moles of metal end groups in such polymers is assumed tobe the number of moles of the metal utilized in the initiator. It is, ofcourse, possible to add greater than a stoichiometric amount of theterminator of formula I. However, the utilization of greater amounts isnot beneficial to final polymer properties. Nevertheless, in many casesit will be desirable to utilize a slight excess of the terminator offormula I to ensure that at least a stoichiometric amount is actuallyemployed or to control the stoichiometry of the functionalizationreaction. In most cases from about 0.8 to about 1.1 moles of theterminator of formula I will be utilized per mole of metal end groups inthe living polymer being treated. In the event that it is not desired tofunctionalize all of the metal terminated chain ends in a rubberypolymer then, of course, lesser amounts of the terminator of formula Ican be utilized.

The terminator of formula I will react with the metal terminated livingrubbery polymer over a very wide temperature range. For practicalreasons, the functionalization of such living rubbery polymers willnormally be carried out at a temperature within the range of 0° C. to150° C. In order to increase reaction rates, in most cases it will bepreferred to utilize a temperature within the range of 20° C. to 100° C.with temperatures within the range of 50° C. to 80° C. being mostpreferred. The capping reaction is very rapid and only very shortreaction times within the range of 0.5 to 4 hours are normally required.However, in some cases reaction times of up to about 24 hours may beemployed.

After the functionalization reaction is completed, it will normally bedesirable to quench any living chains which remain. This can beaccomplished by adding an alcohol, such as methanol or ethanol, to thepolymer cement after the functionalization reaction is completed inorder to eliminate any living polymer that was not consumed by thereaction with the terminator of formula I. The end-group functionalizedpolydiene rubber can then be recovered from the solution utilizingstandard techniques.

The functionalized polymer may be compounded into a rubber composition.The rubber composition may optionally include, in addition to thefunctionalized polymer, one or more rubbers or elastomers containingolefinic unsaturation. The phrases “rubber” or “elastomer containingolefinic unsaturation” or “diene-based elastomer” are intended toinclude both natural rubber and its various raw and reclaim forms aswell as various synthetic rubbers. In the description of this invention,the terms “rubber” and “elastomer” may be used interchangeably, unlessotherwise prescribed. The terms “rubber composition,” “compoundedrubber” and “rubber compound” are used interchangeably to refer torubber which has been blended or mixed with various ingredients andmaterials and such terms are well known to those having skill in therubber mixing or rubber compounding art. Representative syntheticpolymers are the homopolymerization products of butadiene and itshomologues and derivatives, for example, methylbutadiene,dimethylbutadiene and pentadiene as well as copolymers such as thoseformed from butadiene or its homologues or derivatives with otherunsaturated monomers. Among the latter are acetylenes, for example,vinyl acetylene; olefins, for example, isobutylene, which copolymerizeswith isoprene to form butyl rubber; vinyl compounds, for example,acrylic acid, acrylonitrile, which polymerize with butadiene to formNBR, methacrylic acid and styrene, the latter compound polymerizing withbutadiene to form SBR, as well as vinyl esters and various unsaturatedaldehydes, ketones and ethers, e.g., acrolein, methyl isopropenyl ketoneand vinylethyl ether. Specific examples of synthetic rubbers includeneoprene (polychloroprene), polybutadiene (includingcis-1,4-polybutadiene), polyisoprene (including cis-1,4polyisoprene),butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutylrubber, styrene/isoprene/butadiene rubber, copolymers of 1,3-butadieneor isoprene with monomers such as styrene, acrylonitrile and methylmethacrylate, as well as ethylene/propylene terpolymers, also known asethylene/propylene/diene monomer (EPDM), and in particular,ethylene/propylene/dicyclopentadiene terpolymers. Additional examples ofrubbers which may be used include alkoxy-silyl end functionalizedsolution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupledand tin-coupled star-branched polymers. The preferred rubber orelastomers are polyisoprene (natural or synthetic), polybutadiene andSBR.

In one aspect, the at least one additional rubber is preferably of atleast two of diene based rubbers. For example, a combination of two ormore rubbers is preferred such as cis 1,4-polyisoprene rubber (naturalor synthetic, although natural is preferred), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion and solution polymerizationderived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers.

In one aspect of this invention, an emulsion polymerization derivedstyrene/butadiene (E-SBR) might be used having a relatively conventionalstyrene content of about 20 to about 28 percent bound styrene or, forsome applications, an E-SBR having a medium to relatively high boundstyrene content, namely, a bound styrene content of about 30 to about 45percent.

By emulsion polymerization prepared E-SBR, it is meant that styrene and1,3-butadiene are copolymerized as an aqueous emulsion. Such are wellknown to those skilled in such art. The bound styrene content can vary,for example, from about 5 to about 50 percent. In one aspect, the E-SBRmay also contain acrylonitrile to form a terpolymer rubber, as E-SBAR,in amounts, for example, of about 2 to about 30 weight percent boundacrylonitrile in the terpolymer.

Emulsion polymerization prepared styrene/butadiene/acrylonitrilecopolymer rubbers containing about 2 to about 40 weight percent boundacrylonitrile in the copolymer are also contemplated as diene basedrubbers for use in this invention.

The solution polymerization prepared SBR (S-SBR) typically has a boundstyrene content in a range of about 5 to about 50, preferably about 9 toabout 36, percent. The S-SBR can be conveniently prepared, for example,by organo lithium catalyzation in the presence of an organic hydrocarbonsolvent.

In one embodiment, cis 1,4-polybutadiene rubber (BR) may be used. SuchBR can be prepared, for example, by organic solution polymerization of1,3-butadiene. The BR may be conveniently characterized, for example, byhaving at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber arewell known to those having skill in the rubber art.

The term “phr” as used herein, and according to conventional practice,refers to “parts by weight of a respective material per 100 parts byweight of rubber, or elastomer.”

The rubber composition may also include up to 70 phr of processing oil.Processing oil may be included in the rubber composition as extendingoil typically used to extend elastomers. Processing oil may also beincluded in the rubber composition by addition of the oil directlyduring rubber compounding. The processing oil used may include bothextending oil present in the elastomers, and process oil added duringcompounding. Suitable process oils include various oils as are known inthe art, including aromatic, paraffinic, naphthenic, vegetable oils, andlow PCA oils, such as MES, TDAE, SRAE and heavy naphthenic oils.Suitable low PCA oils include those having a polycyclic aromatic contentof less than 3 percent by weight as determined by the IP346 method.Procedures for the IP346 method may be found in Standard Methods forAnalysis & Testing of Petroleum and Related Products and BritishStandard 2000 Parts, 2003, 62nd edition, published by the Institute ofPetroleum, United Kingdom.

The rubber composition may include from about 10 to about 150 phr ofsilica. In another embodiment, from 20 to 80 phr of silica may be used.

The commonly employed siliceous pigments which may be used in the rubbercompound include conventional pyrogenic and precipitated siliceouspigments (silica). In one embodiment, precipitated silica is used. Theconventional siliceous pigments employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate.

Such conventional silicas might be characterized, for example, by havinga BET surface area, as measured using nitrogen gas. In one embodiment,the BET surface area may be in the range of about 40 to about 600 squaremeters per gram. In another embodiment, the BET surface area may be in arange of about 80 to about 300 square meters per gram. The BET method ofmeasuring surface area is described in the Journal of the AmericanChemical Society, Volume 60, Page 304 (1930).

The conventional silica may also be characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, alternatively about 150 to about 300.

The conventional silica might be expected to have an average ultimateparticle size, for example, in the range of 0.01 to 0.05 micron asdetermined by the electron microscope, although the silica particles maybe even smaller, or possibly larger, in size.

Various commercially available silicas may be used, such as, only forexample herein and without limitation, silicas commercially availablefrom PPG Industries under the Hi-Sil trademark with designations 210,243, etc; silicas available from Rhodia, with, for example, designationsof Z1165MP and Z165GR and silicas available from Degussa AG with, forexample, designations VN2 and VN3, etc.

Commonly employed carbon blacks can be used as a conventional filler inan amount ranging from 10 to 150 phr. In another embodiment, from 20 to80 phr of carbon black may be used. Representative examples of suchcarbon blacks include N110, N121, N134, N220, N231, N234, N242, N293,N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539,N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907,N908, N990 and N991. These carbon blacks have iodine absorptions rangingfrom 9 to 145 g/kg and DBP number ranging from 34 to 150 cm³/100 g.

Other fillers may be used in the rubber composition including, but notlimited to, particulate fillers including ultra high molecular weightpolyethylene (UHMWPE), crosslinked particulate polymer gels including,but not limited to, those disclosed in U.S. Pat. Nos. 6,242,534;6,207,757; 6,133,364; 6,372,857; 5,395,891; or 6,127,488, andplasticized starch composite filler including but not limited to thatdisclosed in U.S. Pat. No. 5,672,639. Such other fillers may be used inan amount ranging from 1 to 30 phr.

In one embodiment, the rubber composition may contain a conventionalsulfur containing organosilicon compound. In one embodiment, the sulfurcontaining organosilicon compounds are 3,3′-bis(trimethoxy or triethoxysilylpropyl) polysulfides. In one embodiment, the sulfur containingorganosilicon compounds are 3,3′-bis(triethoxysilylpropyl) disulfideand/or 3,3′-bis(triethoxysilylpropyl) tetrasulfide.

In another embodiment, suitable sulfur containing organosiliconcompounds include compounds disclosed in U.S. Pat. No. 6,608,125. In oneembodiment, the sulfur containing organosilicon compounds includes3-(octanoylthio)-1-propyltriethoxysilane,CH₃(CH₂)₆C(═O)—S—CH₂CH₂CH₂Si(OCH₂CH₃)₃, which is available commerciallyas NXT™ from Momentive Performance Materials.

In another embodiment, suitable sulfur containing organosiliconcompounds include those disclosed in U.S. Patent Publication No.2003/0130535. In one embodiment, the sulfur containing organosiliconcompound is Si-363 from Degussa.

The amount of the sulfur containing organosilicon compound in a rubbercomposition will vary depending on the level of other additives that areused. Generally speaking, the amount of the compound will range from 0.5to 20 phr. In one embodiment, the amount will range from 1 to 10 phr.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials suchas, for example, sulfur donors, curing aids, such as activators andretarders and processing additives, such as oils, resins includingtackifying resins and plasticizers, fillers, pigments, fatty acid, zincoxide, waxes, antioxidants and antiozonants and peptizing agents. Asknown to those skilled in the art, depending on the intended use of thesulfur vulcanizable and sulfur-vulcanized material (rubbers), theadditives mentioned above are selected and commonly used in conventionalamounts. Representative examples of sulfur donors include elementalsulfur (free sulfur), an amine disulfide, polymeric polysulfide andsulfur olefin adducts. In one embodiment, the sulfur-vulcanizing agentis elemental sulfur. The sulfur-vulcanizing agent may be used in anamount ranging from 0.5 to 8 phr, alternatively with a range of from 1.5to 6 phr. Typical amounts of tackifier resins, if used, comprise about0.5 to about 10 phr, usually about 1 to about 5 phr. Typical amounts ofprocessing aids comprise about 1 to about 50 phr. Typical amounts ofantioxidants comprise about 1 to about 5 phr. Representativeantioxidants may be, for example, diphenyl-p-phenylenediamine andothers, such as, for example, those disclosed in The Vanderbilt RubberHandbook (1978), Pages 344 through 346. Typical amounts of antiozonantscomprise about 1 to 5 phr. Typical amounts of fatty acids, if used,which can include stearic acid comprise about 0.5 to about 3 phr.Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typicalamounts of waxes comprise about 1 to about 5 phr. Often microcrystallinewaxes are used. Typical amounts of peptizers comprise about 0.1 to about1 phr. Typical peptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the resultingvulcanizate. In one embodiment, a single accelerator system may be used,i.e., primary accelerator. The primary accelerator(s) may be used intotal amounts ranging from about 0.5 to about 4, alternatively about 0.8to about 1.5, phr. In another embodiment, combinations of a primary anda secondary accelerator might be used with the secondary acceleratorbeing used in smaller amounts, such as from about 0.05 to about 3 phr,in order to activate and to improve the properties of the vulcanizate.Combinations of these accelerators might be expected to produce asynergistic effect on the final properties and are somewhat better thanthose produced by use of either accelerator alone. In addition, delayedaction accelerators may be used which are not affected by normalprocessing temperatures but produce a satisfactory cure at ordinaryvulcanization temperatures. Vulcanization retarders might also be used.Suitable types of accelerators that may be used in the present inventionare amines, disulfides, guanidines, thioureas, thiazoles, thiurams,sulfenamides, dithiocarbamates and xanthates. In one embodiment, theprimary accelerator is a sulfenamide. If a second accelerator is used,the secondary accelerator may be a guanidine, dithiocarbamate or thiuramcompound.

The mixing of the rubber composition can be accomplished by methodsknown to those having skill in the rubber mixing art. For example, theingredients are typically mixed in at least two stages, namely, at leastone non-productive stage followed by a productive mix stage. The finalcuratives including sulfur-vulcanizing agents are typically mixed in thefinal stage which is conventionally called the “productive” mix stage inwhich the mixing typically occurs at a temperature, or ultimatetemperature, lower than the mix temperature(s) than the precedingnon-productive mix stage(s). The terms “non-productive” and “productive”mix stages are well known to those having skill in the rubber mixingart. The rubber composition may be subjected to a thermomechanicalmixing step. The thermomechanical mixing step generally comprises amechanical working in a mixer or extruder for a period of time suitablein order to produce a rubber temperature between 140° C. and 190° C. Theappropriate duration of the thermomechanical working varies as afunction of the operating conditions, and the volume and nature of thecomponents. For example, the thermomechanical working may be from 1 to20 minutes.

The rubber composition may be incorporated in a variety of rubbercomponents of the tire. For example, the rubber component may be a tread(including tread cap and tread base), sidewall, apex, chafer, sidewallinsert, wirecoat or innerliner. In one embodiment, the component is atread.

The pneumatic tire of the present invention may be a race tire,passenger tire, aircraft tire, agricultural, earthmover, off-the-road,truck tire, and the like. In one embodiment, the tire is a passenger ortruck tire. The tire may also be a radial or bias.

Vulcanization of the pneumatic tire of the present invention isgenerally carried out at conventional temperatures ranging from about100° C. to 200° C. In one embodiment, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air. Such tires can be built,shaped, molded and cured by various methods which are known and will bereadily apparent to those having skill in such art.

This invention is illustrated by the following examples that are merelyfor the purpose of illustration and are not to be regarded as limitingthe scope of the invention or the manner in which it can be practiced.Unless specifically indicated otherwise, parts and percentages are givenby weight.

Example 1

Trisopropanolamine (TIPA, 1.00 eq, from Aldrich), vinyltriethoxysilane(V-TEOS, 1.02 eq, from Aldrich) and sodium hydroxide (2 percent, fromAldrich) were mixed in a 1-liter 3-neck round bottom flask equipped withvacuum distillation apparatus. Over a four-hour period, the mixture washeated from 30 to 60° C. and ethanol produced from the reaction wasremoved under reduced pressure of 200 to 20 mm Hg. The crude solid wasthen recrystallized from hexanes. Drying under vacuum gave 201.2 g (87percent yield) of the purified 1-vinyl-3,7,10-trimethylsilatrane (VPOS)as a white crystalline solid. ¹H-NMR and ¹³C-NMR spectroscopy analysishas shown larger than 95 percent purity of the desired product. MeltingPoint: 98-101° C.

Example 2

In this example, bench scale synthesis of a functionalized elastomer isillustrated. Polymerizations were performed in a 1-quart bottle andheated by means of a 65° C. water bath. Monomer premix of styrene andbutadiene (360.5 g, 15 wt percent) was charged into reactor with hexaneas solvent followed by addition of modifier (TMEDA, 0.185 mL) andinitiator (n-butyllithium, 0.31 mL, 1.45 mol/L). When the conversion wasabove 98 percent (2 hours), the polymerizations were terminated withfunctional terminators of Example 1. Hexane was evaporated by droppingpolymer cement into hot water. Sample was dried in air for one day andthen in 70° C. oven for 2 hours.

The polymers obtained were characterized using different techniques, forexample, size exclusion chromatography (SEC) for determination ofmolecular weight, dynamic scanning calorimetry (DSC) for determinationof T_(g), IR for determining cis, trans, styrene and vinyl content, andMooney viscosity measurements with results given in Tables 1 and 2.

TABLE 1 Polymer Sample Overall Mn (kg/mol) PDI Sulfanylsilane-SBR¹(comparative) 206 1.29 SBR² (control) 181 1.04 VPOS-SBR-A³ 255 1.51VPOS-SBR-B⁴ 261 1.48 ¹Sulfanylsilane functionalized solution polymerizedstyrene-butadiene rubber, available commercially as Sprintan ® SLR 4602,from Styron ²Solution polymerized styrene-butadiene rubber terminatedusing isopropanol ³Solution polymerized styrene-butadiene terminatedwith 0.5 eq terminator of Example 1 ⁴Solution polymerizedstyrene-butadiene terminated with 0.75 eq terminator of Example 1

TABLE 2 Tg Polymer Inflection, Sample Mooney Cis Trans Styrene Vinyl¹ °C. SBR-1: 67 15 15 20 50 −22 Sulfanylsilane- SBR (compar- ative) SBR-2:Non- 65 16 15 20 49 −21 functionalized SBR (control) SBR-3: VPOS- 62 1614 20 51 −21 SBR-A SBR-4: VPOS- 58 15 15 20 52 −21 SBR-B ¹Vinyl contentexpressed as weight percent based on total polymer weight

Example 3

The VPOS-functionalized SBR copolymers of Example 2 (SBR-3 and SBR-4) aswell as control (SBR-2) and a comparative sulfanylsilane functionalizedSBR (SBR-1) were subsequently compounded.

Rubber compounds were mixed in a 3-piece 75 mL CW Brabender® mixerequipped with Banbury® rotor. Each SBR sample was mixed with additivesin a two-stage mix procedure as shown in Table 3, with all amounts givenin parts by weight, per 100 parts by weight of elastomer (phr). In thenon-productive mix stage, compounds were mixed for 4 minutes at 100 rpmusing 120° C. as starting temperature. Productive mixes were carried outat an 80° C. starting temperature and 60 rpm with mix time of 3 minute.

The compounds were tested for rheology properties using an RPA 2000®from Alpha Technology. Productive compounds were first heated to 100° C.and the storage modulus was measured at a frequency of 0.83 Hz and 15percent strain in order to determine the processability of thecompounds. Subsequently the compounds were cured at 160° C. for 16minutes at the lowest possible strain (0.7 percent) to mimic a staticcure. Then the compounds were cooled to 100° C., and a subsequent strainsweep is performed. Results are shown in Table 4 and FIGS. 1 to 3.

TABLE 3 SBR 100 Silica 65 Silane coupling agent 5.2 Stearic acid 2 Oil20 Antidegradants 2.75 Waxes 1.5 Sulfur 1.7 Accelerators 3.1

TABLE 4 Sample No. SBR-1 SBR-2 SBR-3 SBR-4 Uncured G′ at 0.83 Hz (kPa)321 259 312 319 G′ 1% (kPa) 3873 5637 3767 3614 Tan delta 10% 0.088 0.110.1 0.092 300% M (MPa) 9.35 7.62 8.9 9.08 Tensile strain at Max (%) 446493 454 483 300/100 modulus 4.14 3.39 3.8 3.83

As seen in FIG. 1, MDR curves show that samples were vulcanized in asimilar rate, which indicates that the silatrane functional groups ofthe polymer (SBR-3 and SBR-4) do not notably interfere with thevulcanization process compared to non-functionalized control.

The storage modulus, RPA G′ curves in FIG. 2 indicate an increase inpolymer filler interaction for samples containing silatrane functionalgroups (SBR-3 and SBR-4), compared to non-functionalized control, SBR-2.Such increased polymer filler interaction is shown as reduced Payneeffect. The Payne effect is the nonlinear dynamic mechanical property ofelastomers in the presence of filler first studied by Payne, Appl.Polym. Sci., 6, 57 (1962). Generally it is associated with the breakdownand agglomeration of filler particles. In the presence of functionalizedelastomer, the interaction of polar functional groups and fillerparticles, e.g. silica, facilitates the filler network breakdown, whichmay lead to better filler dispersion. Tan delta curves (FIG. 3) haveshown lower values for samples containing functionalized polymerdisclosed herein (SBR-3 and SBR-4), compared to non-functionalizedcontrol, SBR-2. Lower tan delta may also indicate better polymer fillerinteraction, as well as better silica dispersion.

While certain representative embodiments and details have been shown forthe purpose of illustrating the subject invention, it will be apparentto those skilled in this art that various changes and modifications canbe made therein without departing from the scope of the subjectinvention.

What is claimed is:
 1. A functionalized elastomer comprising thereaction product of a living anionic elastomeric polymer and apolymerization terminator of formula I

wherein R¹ is C1 to C4 linear alkanediyl, or C1 to C4 branchedalkanediyl; X¹, X², X³ in formula I may be independently 0, S, a groupof formula II, or a group of formula III;

where R² is C1 to C18 linear or branched alkyl; and Z is —R³—CH═CH—R⁴,where R³ is a covalent bond or C1 to C18 linear or branched alkanediyl,and R⁴ is a hydrogen or C1 to C18 linear or branched alkyl; wherein Q isnitrogen.
 2. The functionalized elastomer of claim 1, wherein the livinganionic elastomer is derived from at least one diene monomer andoptionally at least one vinyl aromatic monomer.
 3. The functionalizedelastomer of claim 1, wherein the living anionic elastomer is derivedfrom at least one of isoprene and butadiene, and optionally fromstyrene.
 4. The functionalized elastomer of claim 1, wherein the livinganionic elastomer is derived from butadiene and styrene.
 5. Thefunctionalized elastomer of claim 1, wherein the polymerizationterminator of formula I is of the following structure


6. A rubber composition comprising the functionalized elastomer ofclaim
 1. 7. The rubber composition of claim 6, further comprisingsilica.
 8. A pneumatic tire comprising the rubber composition of claim7.